Field of the Invention
The present invention relates to an optical scanning device provided in an image forming apparatus.
Description of the Related Art
Conventionally, an image forming apparatus using an electrophotographic method scans a photosensitive drum whose surface has been charged to a uniform potential with a light beam corresponding to image information emitted from an optical scanning device, to form an electrostatic latent image. The formed electrostatic latent image is developed by a developer (toner) into a visible image. After a toner image as the visible image is transferred to a sheet, the unfixed toner image is fixed to the sheet by a fixing device, and the sheet is discharged. The optical scanning device, which performs scanning with the light beam, includes a deflection device including a rotating polygonal mirror for deflecting a light beam emitted from a semiconductor laser serving as a light emission source, and an optical system including an optical lens (fθ lens) and a reflecting mirror. In recent years, a demand for high-speed recording has increased in the image forming apparatus. A scanning speed in the optical scanning device has been increasing, i.e., high-speed rotation of the rotating polygonal mirror in the deflection device has been progressing. When the rotating polygonal mirror rotates at high speed, a positive pressure area and a negative pressure area occur on a mirror surface of the rotating polygonal mirror, and dirt such as minute dust and mist in air adheres to the mirror surface corresponding to the negative pressure area. When the dirt adheres to the rotating polygonal mirror, the reflectance of a portion to which the dirt has adhered is reduced. As a result, the light amount of the light beam emitted from the optical scanning device and deflected by the rotating polygonal mirror is reduced, which may cause inferior writing into the photosensitive drum, and may further cause deterioration in image quality on the sheet to which an image formed on the photosensitive drum is transferred.
To address such an issue, in the conventional optical scanning device, the following configuration ensures tight sealing of the optical scanning device. More specifically, an opening provided in an upper part of a housing (hereinafter referred to as an optical box) including an optical component is covered with a cover component (hereinafter referred to as an upper cover) covering the opening. At a portion where the optical box and the upper cover are in contact with each other, a sealing member including a soft sealing member such as a foam member is sandwiched therebetween. Further, the upper cover and the optical box are fastened to each other using a snap fit or a screw to press the sealing member in the sealing member, so as to ensure the tight sealing of the optical scanning device.
However, in this configuration, the upper cover may be deformed by a repulsive force of the pressed sealing member, and the sealing member may be worn out by being pressed continuously. Accordingly, the sealing property of the optical scanning device is deteriorated with the deformation of the upper cover and the wear-out of the sealing member. To prevent the deterioration in the tightness of the optical box, measures to reduce the deformation of the upper cover and the wear-out of the sealing member as much as possible have been proposed. For example, Japanese Patent Application Laid-Open No. 2014-12368 discusses an optical box having a plurality of fixing seating surfaces provided to fasten an upper cover to an optical box with a screw. In the optical box, the fixing seating surfaces to which the upper cover is fixed with a screw include high and low surfaces. The high fixed seating surface and the upper cover are fastened with a screw when the optical box starts to be used. The fixed seating surface is removable. When a sealing member is worn out, the upper cover is reassembled. At this time, the high fixed seating surface so far used is removed, and the upper cover is fixed with a screw to the low fixed seating surface. In such a manner, the upper cover can be fastened to the optical box even with the sealing member worn out. Further, when the high fixed seating surface is removed, and the upper cover is fixed with a screw to the low fixed sealing surface, the upper cover can be prevented from being deformed by a repulsive force from the fixed seating surfaces.
However, the above-described method does not reach a fundamental solution to the deformation of the upper cover caused by the repulsive force of the sealing member. A gap between the sealing member and the upper cover may occur with the deformation of the upper cover, other members may be separated with the deformation of the upper cover, and the sealing member may be separated from the upper cover. Therefore, measures against a decrease in dust-proof performance are insufficient.